I was the glass-half-full optimist who bought the sad looking KB dual standard television with no LOPT at the NVCF for a tenner, mainly because I liked the look of it and it was a model I'd not seen before (although now I've written that down it looks like a bit of a poor excuse!)

Anyway sure enough a chassis has turned up complete with LOPT- albeit an unknown quantity. Now this donor chassis is a VC53 whereas that in the set itself is a VC4. It looks identical with the exception of having a rotary knob for the system switch, as opposed to the older style rocker switch. I'd be interested to know what electrical differences there may be, if any. The LOPT looks to be a direct swap, although one concern is whether the donor chassis is from a 23" or a 19" set, the former presumably having slightly higher EHT.

Hi Steve, the VC53 line output transformer will work in the VC4, the circuits are very similar.The VC4 range of sets were introduced in 1966. Possibly the best looking KB and RGD models because of the mask which hides the implosion protection of Mullard AW47-11 Panorama CRTs although I notice your set has a Brimar tube. It's likely the tube is a rebranded Mazda. Brimar became part of Thorn-AEI Valves and Tubes Ltd.

Servicing information for the VC4 can be found in the 1967/68 R & T servicing book. The text informs us that the VC4 is similar to the VC3, different tuners. No indication if there is any component or circuit differences between 19 and 23" models. I don't remember there ever being any. I had lots of these sets on rental.

The LOPT looks to be a direct swap, although one concern is whether the donor chassis is from a 23" or a 19" set, the former presumably having slightly higher EHT.

Steve

Hi Steve,

I doubt there will be any difference, or any problems.. As I recall, my granddad used to swap chassis and components of various makes and models without difficulty.

For example, he once had a quantity of EKCO and Ferranti 405 line sets, all the same chassis, but came in 17" and 21" versions.. The sets were made up according to which had the best CRT and/or best cabinet.. The chassis from a 17" would perform equally well with either size CRT, and vice versa.

Same rule applied to Bush TV53 and TV56, where the power/timebase chassis were sometimes exchanged - whether from a 14" TV53, or a 17" TV56, they were mutually interchangeable.. It also applied to the LOPT itself, often robbed out of one chassis and reinstalled in another - CRT size was never even a consideration.

I would expect the same will apply here too, setting up/adjustment of the set after fitting, notwithstanding.

VC4 1966- so that's a 'D' reg then (just equating it into old car terms!)

Thanks Till and Marion for your replies. I'm daring to be hopeful that this set may be a runner, unless of course the scrap chassis came about due to LOPT failure. I'm sure all be become apparent very shortly...

Rich's recent work on his RGD VC1 series set reminded me it was about time I returned to my VC4. The attached photo may not look much but it represents something of a momentous breakthrough. It came to fruition when I fitted the LOPT from the scrap chassis I was given. I very gradually applied power, keeping an eye on HT volts, valve heaters and smoke etc... At 200v input a line whistle started up and a raster appeared. Clunking through the VHF tuner provides reassuring splashes and dots. It lives!

The picture shows the KB running with a 200v input, hence dim raster captured under romantic lighting levels and soft focus.... I'm being cautious as the set obviously hasn't been run for many years and all the caps are the originals so I don't want to push my luck. If I'm feeling brave I'll give it the full beans later.

It looks promising Steve, I have a set exactly the same as yet unrestored. I had to re glue the cabinet when I first got it as all the glue had dried out and the top and one side were completely loose.I would replace the capacitors in the line stage before running it too long. You will probably find the primary gets very hot after a while. The s correction capacitor in the RGD VC1 was reading three times the original value, every capacitor I have checked so far has been miles off value with some so leaky they read in the 100s ohms range on my AVO 8. The Mullard Mustards are usually OK. I have seen a couple though that the ends were coming off so it's always best to check.Well done for saving such a poor old thing sometimes the 'wrecks' are the most fun!Rich.

Great progress indeed! The image reminds me of a 405-line display I've seen on a GEC 2028. That turned out to be due to the switching arrangement at the underside of the main PCB, in other words set for 625 with completely wrong scan correction on 405. The oval Test Card reminded me of Looby Loo of "Andy Pandy" fame. Always wondered why she had an oval shaped head and why she had to go back to her cot when Andy and Teddy returned.....

And here we go... Now looking much better. The 2.7k resistor in the EHT rectifier base had doubled in value. Replacing it brought the width back within sane limits. A new DY86 (DY802 actually) cured the ballooning and finally renewing the 1.5M resistor feeding the height control restored some headroom. Oddly the linearity has been fine from the word go.

The crt ain't going to win any awards, but may improve with use. Still some work to do, but I'm delighted to have any results at all from this £10 wreck!

I was the glass-half-full optimist who bought the sad looking KB dual standard television with no LOPT at the NVCF for a tenner, mainly because I liked the look of it and it was a model I'd not seen before (although now I've written that down it looks like a bit of a poor excuse!)Steve

You are absolutely right there Terry, well spotted. In fact the linearity sleeve had been pulled a long way out by persons unknown. A mark in the dirt showed where it used to be so I matched it up to that and line linearity is better now. In fact I found myself using a bit of paper to compare sizes of the squares. Good grief.

The diagonal gratings are still a bit bendy but I notice that the plastic former carrying the scan coils is a bit distorted at the top. That's my excuse anyhow. I may try swapping the coils from another 19" KB I have lying around.

I now notice from my photo that the vertical linearity is in need of a slight tweak too.

The set is still in filthy 'as found' condition, so I have some serious cleaning to do, followed by a light sand and some Danish oil for the cabinet.

Colourstar wrote:The diagonal gratings are still a bit bendy but I notice that the plastic former carrying the scan coils is a bit distorted at the top.

Yes, Steve. It is also responsible for the picture not being square. Although the horizontal lines are clearly horizontal, you can see from the picture that the vertical sides are tilted.

Take another look at the scan coils - they may have correction magnets fitted - vertical rods in brass holders at the left and right. If you have them on yours, try bending them in and out - I would suggest that yours need to be bent outwards - and also twist them slightly, while looking at the results in the mirror.

Not forgetting that most people "back in the day" wouldn't be viewing with such a critical eye - try watching an episode of "The Avengers" "The Saint" or "A Man Called Ironside" etc, and I doubt you would really notice the geometric aberrations.. That said though, it could still stand a little improvement.

I find you can spend literally hours tweaking away at the test card until you send yourself mad. I've got the linearity as good as I can manage now. It's a shame the crt in this KB is decidedly tired. I wish I'd thought to ask Marc to do a clean & balance on it when he was here, as that seems to work wonders with borderline tubes. I spent some time the other day cleaning the filthy control panel and attacking the grimy control knobs with an old toothbrush and some soap.

For now I shall just enjoy some vintage programming, which is what it's all about isn't it?